As the realization of an ubiquitous society approaches, there are great hopes for the development of wearable display devices. A wearable display device is a flexible device consisting of a flexible substrate and a display element formed thereon. Examples of such display devices include liquid crystal display elements, organic electroluminescent (organic EL) elements, and paper-like displays (electronic paper).
For example, a polymeric material such as polyimide has been used for the flexible substrate. Such substrates can be bent within a range of elastic deformation without generating plastic deformation (permanent deformation) up to a curvature radius of about several mm. However, bending beyond a range of elastic deformation leads to permanent deformation, which in turn causes whitening of the deformed members.
For example, an inorganic insulating film and an indium tin oxide (ITO) electrode have been used in many flexible display devices. Alternatively, a thin-film transistor is formed on a flexible substrate in active-display devices. Thus, bending of a flexible display device beyond a particular curvature radius leads to breakdown of the insulating film and the electrode.
The following Patent Document 1 discloses a flexible thin-film circuit board highly resistant to bending stress. In the thin-film circuit board disclosed in Patent Document 1, an inorganic insulating film in an island pattern is disposed over the electronic element such as of thin film transistor. The inorganic insulating film and wiring are covered with a resin film additionally.
The inorganic insulating film higher in rigidity than the organic insulating films protects the electronic element by covering the electronic element. When bending stress is applied to the thin-film circuit board, the substrate and the resin film can be bent together according to the bending stress applied, because the inorganic insulating film is patterned in an island structure.
The invention disclosed in Patent Document 1 allows protection of the electronic element from bending stress, but the region where no electronic element is formed may be bent beyond the elastic deformation range. The bending members cause permanent deformation and whitening of the flexible substrate. For that reason, the operator should be careful enough in handling the flexible base material not to generate permanent deformation by bending.
An object of the present invention is to provide a flexible base material highly resistant to excessive deformation and stress that may cause permanent deformation, and a flexible image-displaying device using the same.
[Patent Document 1]
JP-A No. 2004-101976